Efficient n-type doping was not established since the dopants dose not dissolve in same organic solutions of polymer semiconductors. Evaporative Spray Deposition using Ultra-dilute Solution (ESDUS) method enabled it recently. We have already reported efficient n-type doping of poly(2-methoxy-5-(2’-methyl-hexyloxy)-p- phenylenevinylene) (MEH-PPV: LUMO: 3.1 eV, HOMO: 5.2 eV). The high doping efficiency as much as 15% was realized. In organic devices composed of non-doped organic semiconductors, electron injection barrier is basically equal to the gap between LUMO of the organic semiconductor and work function of the el ectrode. It is still open question how the barrier is formed in the n-doped polymer/electrode. The metal/semiconductor junction of n-doped polymer has not been studied yet. In this research, we have fabricated electron only devices (EOD) of an n-doped polymer semiconductor using electrodes of Al and Ca. The electron injection from Al or Ca was examined.MEH-PPV (Mw = 40,000-70,000 Aldrich) and Cesium carbonate were used as a host polymer and an n-type dopant, respectively. The asymmetric EOD using Al for bottom and top electrodes and and a top Ca electrode having a lower work function (3.0 eV) were fabricated. The current-voltage (J-V) characteristics were measured in vacuum without breaking vacuum after the top electrode deposition. J-V characteristics of asymmetric EOD (Fig. 1), Al(50nm)/MEH-PPV:Cs₂CO₃ (110nm)/Ca(50nm) are fabricated. The current density was drastically increased as the doping concentration increased. The asymmetric EODs, current density in the forward bias was about 1 order of magnitude larger than that in reverse bias at low doping concentration at 0, 0.2, 2.0 wt%.However, the current density was almost overlapped in forward and reverse bias at the doping concentration of 10wt%. The disappearance of the rectification property suggests that the quantum tunneling takes place due to the very thin depletion layer at Al/MEH-PPV junction at the high doping concentration. In order to evaluate depletion layer width on Al/MEH-PPV junction, C-F measurement was carried out. As a result of the calculation, the depletion layer width of the 0.2 wt% doped device was 16.3 nm, the 2.0 wt% doped device was 9.3 nm, and the 10.0 wt% doped device was 3.3 nm. These results suggest that the depletion layer narrows as the doping concentration increases and the rectification property disappears in the 10 wt% doped device by quantum tunneling. The depletion layer width when quantum tunneling was observed in the p-type organic device, Au/ZnPc:0.3%F4-TCNQ/Au, was 5.2nm. Compared with this depletion layer width of 5.2 nm at metal/p-type organic semiconductor junction, it can be said that the value of 3.3 nm calculated this time is sufficiently narrow to observe quantum tunneling.